This invention relates to a method for producing a solar cell from crystalline silicon and a solar cell made of crystalline silicon produced by this method.
Short circuits occur in contacting the base of crystalline silicon solar cells by overcompensation of the n-type electrically active emitter (see FIG. 1). These short circuits are caused by the direct connection of the metallic back contact, which contacts the p-type base through the p+-layer, to the emitter region, which is electrically connected to the surrounding n+-layer.
To eliminate these short circuits in the industrial production of conventional solar cells, the p+n+ junction is insulated by plasma-assisted etching, by mechanical grinding of edges, by applying an insulating layer before the P-diffusion, and by the use of lasers.
In case of more complex cell geometries with interlaced p- and n-type regions (for example like EWT solar cells (J. M. Gee, W. K. Schubert, P. A. Basore; “Emitter Wrap-Through Solar Cell”; 23rd IEEE Photo. Spec. Conf., 1993, pp. 265–270), POWER solar cells (G. Willeke, P. Fath; “The POWER silicon solar cell concept”; 12th EC PVSEC, Amsterdam, 1994, Vol. 1, pp. 766–68), . . . ), the p+n+ junction is insulated on a laboratory scale by:                plasma-assisted etching,        local removal of the backside emitter (e.g. by wafer-sawing or by means of a laser),        using dielectric layers as diffusion barriers combined with photolithographic methods and printing techniques as well as wet-chemical process steps.        
In past years it has been attempted, fruitlessly, both by companies (S. Robert, K. C. Hessman, T. M. Bruton, R. W. Russel, D. W. Cunningham, “Interdigitated-contact Silicon Solar Cells Made without Photolithography”, 2nd World Conference and Exhibition on PVSEC, Vienna 1998, pp. 1449–51) and by leading PV research organizations to produce insulation of p- and n-type layers by discovering analogous methods, for example such as subsequent alloying of Al after P-diffusion.
The drawbacks of the known methods can be summarized as follows:
Time- and cost-intensive additional process steps for separating the p- and n-type regions, especially in case of more complex geometries, are a great drawback in production on an industrial scale. The resultant costs, for example, have so far been one reason why back-contact solar cells have not become accepted in industrial production in spite of their numerous advantages in wiring modules.
Physical Drawbacks
1. Production of open, i.e. unpassivated p-n junctions during mechanical border separation.
2. Surface damage caused by plasma-assisted etching, which has harmful effects on cell quality because of the increased recombination associated with it.
3. The space charge zone is located directly on the cell surface from local mechanical milling off of the back face of the silicon wafer. The interference levels introduced by the surface are responsible for increased recombination (“Junction Edge Effects”)-> negative effects, especially on VOC and FF.
The problem underlying this invention consists of the fact that the difficulty of insulating p- and n-type doped layers arises with both conventional and novel crystalline silicon solar cells. This problem is solved by the present invention in a simple and elegant manner.